Editing Magdeburg hemispheres (section)

==Overview==
[[Image:Magedurger Halbkugeln Luftpumpe Deutsches Museum.jpg|thumb|left|The original Magdeburg hemispheres and Guericke's vacuum pump in the [[Deutsches Museum]], Munich, Germany]]

The Magdeburg hemispheres, around 50&nbsp;cm (20&nbsp;inches) in diameter,<ref>{{cite web|last=Hablanian|first=M. H.|author2=Hemeon, C. H.|title=Comments about Magdeburg hemispheres reenactment|work=50 years of the AVS|publisher=American Vacuum Society|year=2003|url=http://www2.avs.org/historybook/links/magden.htm|url-status=dead|archiveurl=https://web.archive.org/web/20080803104623/http://www2.avs.org/historybook/links/magden.htm|archivedate=2008-08-03}}</ref><ref>{{cite web|last=Nave|first=C.R.|title=Original Magdeburg Hemispheres|work=Hyperphysics|publisher=Dept. of Physics and Astronomy, Georgia State Univ.|year=2000|url=http://hyperphysics.phy-astr.gsu.edu/Hbase/Kinetic/pmdg.html}}</ref><ref>{{cite web|title=Magdeburg hemispheres|work=Multimedia Catalogue|publisher=Institute and Museum of the History of Science, Florence, Italy|year=2006|url=http://brunelleschi.imss.fi.it/museum/esim.asp?c=500014}}</ref><ref>{{cite book|last=Hall|first=Edwin H.|author2=Bergen, Joseph Y.|title=A Textbook of Physics, 3rd Ed.|publisher = Henry Holt & Co.|year=1903|location=New York|page=[https://archive.org/details/atextbookphysic06berggoog/page/n79 52]|url=https://archive.org/details/atextbookphysic06berggoog|quote=Magdeburg hemispheres.}}</ref> were designed to demonstrate the [[vacuum pump]] that Guericke had invented. One of them had a tube connection to attach the pump, with a valve to close it off.  When the air was sucked out from inside the hemispheres, and the valve was closed, the hose from the pump could be detached, and they were held firmly together by the [[air pressure]] of the surrounding [[Earth's atmosphere|atmosphere]].

The force holding the hemispheres together was equal to the area bounded by the joint between the hemispheres, a [[circle]] with a diameter of 50&nbsp;cm, multiplied by the difference in air pressure between the inside and the outside.  It is unclear how strong a vacuum Guericke's pump was able to achieve, but if it was able to evacuate all of the air from the inside, the hemispheres would have been held together with a force of around {{convert|20|kN|lbf STf|lk=on}},<ref name="Hyperphysics">{{cite web
  | last = Nave
  | first = Carl R.
  | authorlink = 
  | title = Magdeburg Hemispheres
  | work = Hyperphysics
  | publisher = Dept. of Physics and Astronomy, Georgia State Univ.
  | date = 2012
  | url = http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/pmdg.html
  | doi = 
  | accessdate = November 12, 2012}}</ref><ref>Calculated using a diameter of 0.5&nbsp;m with [[atmospheric pressure]]; force is given by
{{math| ''P''<sub>0</sub> * π * ''r''<sup>2</sup>}}, where ''P''<sub>0</sub>=air pressure and ''r''=cross-sectional radius of the hemisphere. Due to the inefficiencies of the vacuum pump, the artificial vacuum was likely much weaker.</ref> equivalent to lifting a car or small [[elephant]]; a dramatic demonstration of the [[atmospheric pressure|pressure of the atmosphere]].